Cell service to thousands of Americans was restored after network outages on Thursday left customers with AT&T and other service providers unable to place calls, send texts or use the internet on their mobile phones.

Why it matters: The disruptions left some people unable to contact emergency services by dialing 911, prompting safety warnings from authorities.

The latest: White House national security spokesperson John Kirby told reporters the FBI and the Department of Homeland Security were looking into the outages, Reuters reports.

• Kirby said U.S. officials have been told AT&T currently has no reason to believe the outages were from a cybersecurity incident.
• He added that the Department of Commerce's communications were affected but the extent of that disruption was not "crippling."
• The Federal Communications Commission said on social media it was also investigating the outages and had been in contact with AT&T.

State of play: AT&T's network suffered the most widespread outages.

• Self-reported AT&T outages surged in the early hours Thursday, reaching more than 73,000 reports just after 8:30am ET, according to the tracking site Downdetector.
• Large swaths of the AT&T outage reports said customers were without signal and unable to use their mobile phones.
• The most reported locations of these outages included cities like Houston, Atlanta and Chicago, among others.

AT&T acknowledged in a statement Thursday morning that some customers were experiencing wireless service interruptions, encouraging those affected to use Wi-Fi calling until service was restored.

• In a subsequent statement, the company noted that while interruptions were ongoing for some customers, "so far three-quarters of our network has been restored."
• "We are working as quickly as possible to restore service to remaining customers," AT&T added.
• Around 2pm, the company said it restored wireless service to all affected customers.

By the numbers: There were over 1,6oo outage reports around 4:30pm ET, according to Downdetector.

Zoom in: Verizon and T-Mobile customers also reported outages Thursday, but at a much lower scale than AT&T.

• More than 4,000 Verizon customers had reported outages just before 8 a.m. ET Thursday, per Downdetector.
• A Verizon spokesperson told Axios that the company's network was "operating normally" and that some customers may have encountered issues when trying to contact customers on another carrier.
• Around 8 a.m. ET, just over 2,000 T-Mobile customers had reported outages, according to Downdetector.

What they're saying: T-Mobile echoed Verizon, telling Axios in a statement that "we did not experience an outage. Our network is operating normally. Down Detector is likely reflecting challenges our customers were having attempting to connect to users on other networks."

The big picture: The San Francisco Fire Department posted on X that it was aware of issues impacting AT&T customers' ability to place 911 calls.

• "The San Francisco 911 center is still operational. If you are an AT&T customer and cannot get through to 911, then please try calling from a landline" or getting ahold of a "friend or family member who is a customer of a different carrier and ask them to call 911 on your behalf."
• Similar warnings were issued from the Irving Police Department in Texas, the Prince William County Police Department in Virginia, and Chicago's Office of Emergency Management & Communications.

Editor's note: This story has been updated to include a statement from AT&T.